1. Field of the Invention
The invention relates to a drive train of a motor vehicle, having an internal combustion engine with a crankshaft, a transmission connected downstream of the internal combustion engine to drive at least one axle of the motor vehicle, and a starter generator assigned to the internal combustion engine.
2. Description of the Related Art
An electrically operated starter generator operates as a motor to start an internal combustion engine. The starter generator also can drive an axle of the motor vehicle together with the internal combustion engine during operation of the drive train as a mild hybrid. In the generator mode, the starter generator is driven by the internal combustion engine and/or via the axle of the motor vehicle.
DE 10 2009 033 633 A1 discloses a drive train with a belt drive that has a belt that is guided over a pulley of the starter generator and functions to drive the generator. The generator can be operated temporarily as a starter motor and is coupled via a freewheel to the generator pulley or an engine crankshaft belt pulley. The freewheel allows the generator to overrun the generator pulley or the crankshaft during the motor mode. As a result, the power flow via the belt drive and the belt drive loading induced by the inherent inertia of the generator can be reduced during an engine start phase, and in phases with a high angular velocity rise of the crankshaft of the internal combustion engine.
JP 58-116229 A describes the drive train of an oil pump of an internal combustion engine. The oil pump is attached either via a belt drive to the internal combustion engine or via a belt drive to an electric machine. To this end, a shiftable clutch is provided between the internal combustion engine and the belt drive that is assigned to the internal combustion engine.
EP 1 079 085 A2 discloses the optional use of an electric machine as starter motor or as generator. The electric machine is attached by a shiftable clutch to a crankshaft of the internal combustion engine. The electric machine also is attached via an auxiliary shaft that is assigned a further shiftable clutch to a transmission that is connected downstream of the internal combustion engine. As a result, when the clutch that is assigned to the auxiliary shaft is closed, the electric machine can be operated in the generator mode via the transmission that is connected downstream of the internal combustion engine.
It is an object of the invention to provide a drive train that ensures an optimum start capability in the case of a cold internal combustion engine and while also providing the possibility to boost the internal combustion engine electrically.